Difference between revisions of "Bond Energy"

Revision as of 16:40, 14 January 2019

Key Stage 4

Meaning

Bond Energy is the energy needed to break a chemical bond between two atoms.

About Bond Energy

When chemical bonds are formed energy is released to the surroundings increasing the temperature. An exothermic process]].

To break chemical bonds energy is needed to separate the atoms, decreasing the temperature of the surroundings. An endothermic process]].

Examples

Some common bond energies are given in the table below.

Bond	Energy in kJ/mol
H-H	436
O=O	498
N≡N	941
C-C	347
C=C	614
C≡C	839
C-H	413
O-H	464
C=O	799
Cl-Cl	243
H-Cl	432
N-H	391

These can be used to calculate the energy released per mole in a chemical reaction.

Example 1


In the reaction between Methane and Oxygen the chemical bonds in the reactants must be broken first before the bonds in the products are formed.

There are 4 C-H bonds and 2 O=O bonds.

4 x 413 + 2 x 498 = 2648kJ

Therefore 2648kJ/mol are needed to break the bonds in the reactants.

There are 2 C=O bonds and 4 O-H bonds.

2 x 799 + 4 x 464 = 3454kJ

Therefore 3454kJ/mol is released when the bonds in the products form.

Once the reaction is complete 806kJ will be released.

Example 2


In the reaction between Hydrogen and Nitrogen the chemical bonds in the reactants must be broken first before the bonds in the products are formed.

There are 3 H-H bonds and 1 N≡N bonds.

3 x 436 + 1 x 941 = 2249kJ

Therefore 2249kJ/mol are needed to break the bonds in the reactants.

There are 6 N-H bonds.

6 x 391 = 2346kJ

Therefore 2346kJ/mol is released when the bonds in the products form.

Once the reaction is complete 97kJ will be released.

@@ Line 50: / Line 50: @@
 | style="height:20px; width:150px; text-align:center;" |391
 |}
+These can be used to calculate the [[energy]] released per [[mole]] in a [[Chemical Reaction|chemical reaction]].
+'''Example 1'''
+{| class="wikitable"
+|-
+|[[File:StructuralDiagramMethane+Oxygen.png|center|500px]]
+|-
+| style="height:20px; width:200px; text-align:center;" |In the [[Chemical Reaction|reaction]] between [[Methane]] and [[Oxygen]] the [[Chemical Bond|chemical bonds]] in the [[reactant]]s must be broken first before the [[Chemical Bond|bonds]] in the [[product]]s are formed.
+|}
+There are 4 C-H [[Chemical Bond|bonds]] and 2 O=O [[Chemical Bond|bonds]].
+x 413 + 2 x 498 = 2648kJ
+Therefore 2648kJ/mol are needed to break the [[Chemical Bond|bonds]] in the [[reactant]]s.
+There are 2 C=O [[Chemical Bond|bonds]] and 4 O-H [[Chemical Bond|bonds]].
+x 799 + 4 x 464 = 3454kJ
+Therefore 3454kJ/mol is released when the [[Chemical Bond|bonds]] in the [[product]]s form.
+Once the [[Chemical Reaction|reaction]] is complete 806kJ will be released.
+'''Example 2'''
+{| class="wikitable"
+|-
+|[[File:StructuralDiagramHydrogen+Nitrogen.png|center|500px]]
+|-
+| style="height:20px; width:200px; text-align:center;" |In the [[Chemical Reaction|reaction]] between [[Hydrogen]] and [[Nitrogen]] the [[Chemical Bond|chemical bonds]] in the [[reactant]]s must be broken first before the [[Chemical Bond|bonds]] in the [[product]]s are formed.
+|}
+There are 3 H-H [[Chemical Bond|bonds]] and 1 N≡N [[Chemical Bond|bonds]].
+x 436 + 1 x 941 = 2249kJ
+Therefore 2249kJ/mol are needed to break the [[Chemical Bond|bonds]] in the [[reactant]]s.
+There are 6 N-H [[Chemical Bond|bonds]].
+x 391 = 2346kJ
+Therefore 2346kJ/mol is released when the [[Chemical Bond|bonds]] in the [[product]]s form.
+Once the [[Chemical Reaction|reaction]] is complete 97kJ will be released.